The invention discloses a turning method for a thin and long threaded shaft. A turning device for the thin and long threaded shaft is used in the method and is installed on a carriage of a lathe. The turning device comprises a base, a guiding sleeve, a telescopic sleeve, a tool reset ring, a thread length control mechanism and a tool assembly. The turning device has the beneficial effects that due to the fact that scale marks are arranged on the surface of the outer circle of the part, close to a shaft ring, of the thin and long shaft, the length value of a to-be-turned thread can be accurately adjusted by adjusting the axial position of a screw sleeve; due to the fact that three sets of turning tools are distributed evenly in the circumferential direction, deformation of the threaded shaft in the turning process is reduced, and the machining quality is ensured; due to the fact that a slope A and a slope C which can be in contact or be separated are arranged, ending machining of the thread can be accurately achieved, and the phenomenon of tool crashing is effectively avoided; and due to the fact that the tool reset ring is arranged, the three sets of turning tools can contract towards the center at the same time, and operation is fast and convenient.